Battery charging system

ABSTRACT

One example includes a battery charging system configured to charge a battery associated with a mobile device. The battery charging system includes a transformer configured to receive an AC charging current via a charging cable at a primary inductor and to generate an AC secondary current at a secondary inductor. The battery charging system also includes a rectifier system configured to rectify and filter the AC secondary current to generate a DC charging current that is provided to charge the battery.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application Ser.No. 62/280,512, filed 19 Jan. 2016, which is incorporated herein in itsentirety.

TECHNICAL FIELD

This disclosure relates generally to electronic systems, and morespecifically to a battery charging system.

BACKGROUND

Wireless electronic devices, such as wireless communications devices(e.g., smart-phones), laptop computers, and tablet computers, arebecoming more prevalent in modern consumer culture. Such devices arebattery-powered, and thus require periodic charging to maintainsufficient battery voltage to operate the respective device. Charging awireless device typically involves providing a DC voltage via a chargingcable (e.g., a universal serial bus (USB) cable), which can take aconsiderable amount of time to charge fully (e.g., more than an hourfrom approximately zero volts). Charging a device in significantly lesstime can be accomplished by delivering a very high current, which isimpractical or prohibitive with connector and cable dimensions oftypical mobile devices. Alternatively, a very high voltage can beimplemented, but such a charging system would require a highlyinefficient step-down DC-DC converter, as well as significantly largecircuit components in the mobile device.

SUMMARY

One example includes a battery charging system configured to charge abattery associated with a mobile device. The battery charging systemincludes a transformer configured to receive an AC charging current viaa charging cable at a primary inductor and to generate an AC secondarycurrent at a secondary inductor. The battery charging system alsoincludes a rectifier system configured to rectify and filter the ACsecondary current to generate a DC charging current that is provided tocharge the battery.

Another example includes a method for charging a battery associated witha mobile device. The method includes receiving a power voltage at an ACadapter and generating an AC charging current based on the power voltagevia a programmable AC current source associated with the AC adapter. TheAC charging current can be provided on a first conductor of a chargingcable that interconnects the AC adapter and the mobile device. Themethod also includes receiving a control voltage on a second conductorof the charging cable. The control voltage can include a voltageassociated with the AC charging current and a DC feedback controlvoltage. The method further includes adjusting an amplitude of the ACcharging current based on an amplitude of the DC feedback controlvoltage.

Another example includes a battery charging system. The system includesan AC adapter comprising a programmable AC current source configured togenerate an AC charging current having an amplitude that is based on anamplitude of a DC feedback control voltage. The system also includes adevice power system associated with a mobile device. The device powersystem includes a transformer configured to receive the AC chargingcurrent via a first conductor of a charging cable at a primary inductorand to generate an AC secondary current at a secondary inductor. Thedevice power system also includes a rectifier system configured torectify the AC secondary current to generate a DC charging current thatis provided to charge a battery associated with the mobile device. Thedevice power system further includes a charge controller configured tomonitor an amplitude of a battery voltage and an amplitude of the ACcharging current and to generate the DC feedback control voltage that isprovided to the AC adapter via a second conductor of the charging cable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a battery charging system.

FIG. 2 illustrates another example of a battery charging system.

FIG. 3 illustrates yet another example of a battery charging system.

FIG. 4 illustrates an example of a method for charging a batteryassociated with a mobile device.

DETAILED DESCRIPTION

This disclosure relates generally to electronic systems, and morespecifically to a battery charging system. The battery charging systemincludes an AC adapter that can receive a power voltage (e.g., an ACline voltage) and is configured to generate a high-frequency (e.g.,greater than approximately 500 kHz) AC charging current. The AC adaptercan include a programmable AC current source to generate the AC chargingcurrent, such that the programmable AC current source can generate theAC charging current at an amplitude that is based on a DC feedbackcontrol voltage. The AC charging current is provided to the mobiledevice via a first conductor of a charging cable (e.g., a universalserial bus (USB) cable, such as a USB Type-C cable).

The mobile device includes a device power system that receives the ACcharging current via the charging cable. The AC charging current isprovided through a primary inductor of a transformer to generate an ACsecondary current via a secondary inductor of the transformer. The ACsecondary current is rectified and filtered to generate a DC chargingcurrent that is provided to charge the battery of the mobile device. Inaddition, the device power system includes a charge controller thatmonitors an amplitude of the AC charging current and an amplitude of thebattery voltage, and generates the DC feedback control voltage at anamplitude that is based on the amplitudes of the AC charging current andthe battery voltage. The DC feedback control voltage is added to the ACcharging current on a second conductor of the charging cable, betweenisolation capacitors associated with the AC adapter and the device powersystem, respectively, such that the DC feedback control voltage can beprovided to the programmable AC current source to set the amplitude ofthe AC charging current in a feedback manner.

FIG. 1 illustrates an example of a battery charging system 10. Thebattery charging system 10 can be implemented for charging a batteryassociated with a variety of different types of mobile devices, such assmart phones, laptop computers, tablet computers, or a variety of otherwireless devices. As described herein, the battery charging system 10can implement very fast charging of the battery (e.g., 1500 mA/h), suchas to charge a battery to approximately 50% of battery capacity withinapproximately five minutes.

The battery charging system 10 includes an AC adapter 12 that isconfigured to generate an AC charging current I_(CHG) in response to apower voltage V_(LINE). As an example, the power voltage V_(LINE) can bean AC line voltage that is provided, for example, from a public utilitypower grid. In the example of FIG. 1, the AC adapter 12 includes aprogrammable AC current source 14 that is configured to generate the ACcharging current I_(CHG) in response to a control voltage V_(CTRL). Asan example, the AC charging current I_(CHG) can have a high frequency(e.g., greater than approximately 500 kHz). As described in greaterdetail herein, the control voltage V_(CTRL) can correspond to a voltageassociated with the AC charging current I_(CHG) and a DC feedbackcontrol voltage. Thus, the programmable AC current source 14 cangenerate the AC charging current I_(CHG) to have an amplitude that isbased on an amplitude of the DC feedback control voltage component.

The AC charging current I_(CHG) is provided on a first conductor of acharging cable 16 that interconnects the AC adapter 12 and a devicepower system 18. As an example, the charging cable 16 can be configuredas a universal serial bus (USB) cable (e.g., a USB Type-C cable). Forexample, the device power system 18 can be provided in the respectivemobile device, such that the charging cable 16 can plug into the mobiledevice to interact with the device power system 18 to charge a battery20 associated with the device power system 18. The device power system18 includes a transformer 22 that is configured to isolate the ACcharging current I_(CHG) from the battery 20 by generating an ACsecondary current. The AC secondary current is rectified and filtered bya rectifier stage 24 to generate a DC charging current that charges thebattery 20. Based on the high frequency and high amplitude of the ACcharging current I_(CHG), the DC charging current can provide very rapidcharging of the battery 20.

The device power system 18 also includes a charge controller 26 that isconfigured to provide feedback control of the AC charging currentI_(CHG). As an example, the charge controller 26 can be configured tomonitor an amplitude of both the AC charging current I_(CHG) and thebattery voltage, and can generate a DC feedback control voltage. The DCfeedback control voltage can be added to the voltage associated with theAC charging current I_(CHG) to provide the control voltage V_(CTRL) thatis provided to the AC adapter 12 via a second conductor of the chargingcable 16. The programmable AC current source 14 can thus adjust anamplitude of the AC charging current I_(CHG) based on an amplitude ofthe DC feedback control voltage in the control voltage V_(CTRL).Accordingly, the programmable AC current source 14 can be configured togenerate the AC charging current I_(CHG) in a feedback manner to providerapid charging of the battery 20.

FIG. 2 illustrates another example of a battery charging system 50. Thebattery charging system 50 can correspond to a more detailed example ofthe battery charging system 10 in the example of FIG. 1. Thus, thebattery charging system 50 can be implemented for charging a batteryassociated with a variety of different types of mobile devices, such assmart phones, laptop computers, tablet computers, or a variety of otherwireless devices in a very rapid manner.

The battery charging system 50 includes an AC adapter 52 that isconfigured to generate an AC charging current I_(CHG) in response to apower voltage V_(LINE). As an example, the power voltage V_(LINE) can bean AC line voltage that is provided, for example, from a public utilitypower grid. In the example of FIG. 2, the AC adapter 52 includes aprogrammable AC current source 54 that is configured to generate the ACcharging current I_(CHG). For example, the programmable AC currentsource 54 can have a compliance range that can span from zero volts toapproximately 40 volts RMS open-circuit, and can be deactivated by theAC adapter 52 in response to an open-circuit condition. As an example,the AC charging current I_(CHG) can have a high frequency (e.g., greaterthan approximately 500 kHz), and can have a sinusoidal or other waveformshape. The AC charging current I_(CHG) is provided on a first conductorof a charging cable 56 that can correspond to any of a variety oftypical charging cables, such as a USB cable (e.g., a USB Type-C cable).

In the example of FIG. 2, the programmable AC current source 54 isconfigured to generate the AC charging current based on a controlvoltage V_(CTRL). As described in greater detail herein, the controlvoltage V_(CTRL) can correspond to a voltage associated with the ACcharging current and with a DC feedback control voltage V_(FB). In theexample of FIG. 2, the AC adapter 52 includes an isolation capacitor C₁that interconnects a second conductor of the charging cable 56 and alow-voltage power rail, demonstrated in the example of FIG. 2 as ground.Therefore, the programmable AC current source 54 can generate the ACcharging current I_(CHG) to have an amplitude that is based on anamplitude of the DC feedback control voltage V_(FB), which cancorrespond to an average voltage across the isolation capacitor C₁.

The charging cable 56 interconnects the AC adapter 52 and a device powersystem 58 that can be located in the respective mobile device.Therefore, the charging cable 56 can be plugged into the mobile deviceto charge a battery B₁ associated with the device power system 58. Inthe example of FIG. 2, the device power system 58 includes a transformerT₁ that includes a primary inductor L₁ and a secondary inductor L₂ thatare magnetically coupled. The AC charging current I_(CHG) is providedfrom the first conductor of the charging cable 56 to the primaryinductor L₁, which thus induces an AC secondary current I_(SEC) in thesecondary inductor L₂. Thus, the transformer T₁ provides isolation ofthe AC charging current I_(CHG) and the battery B₁, such that thebattery B₁ and/or other components of the device power system 58 areprotected from short circuits associated with the AC charging currentI_(CHG). Accordingly, the transformer T₁ of the device power system 58obviates the need for disconnect/isolation switches at the connectionpins associated with the charging cable 56.

The AC secondary current I_(SEC) is provided through a rectifier. In theexample of FIG. 2, the rectifier is formed by a set of transistors N₁,N₂, N₃, and N₄ that can operate as a synchronous bridge, such that thetransistors N₁, N₂, N₃, and N₄ can be switched in response to zerocurrent across the respective transistors N₁, N₂, N₃, and N₄. Therectified AC secondary current I_(SEC) is filtered via an LC filterformed by an inductor L_(F) and a capacitor C_(F) to generate a DCcharging current I_(DC). The DC charging current I_(DC) can thus beprovided to charge the battery B₁. While the rectifier stage in theexample of FIG. 2 is demonstrated as a combination of the synchronousbridge formed by the transistors N₁, N₂, N₃, and N₄ and the LC filterformed by the inductor L_(F) and the capacitor C_(F) (e.g., collectivelycorresponding to the rectifier stage 24 in the example of FIG. 1), it isto be understood that other rectifiers and/or filters can be implementedto generate the DC charging current I_(DC) based on the AC secondarycurrent I_(SEC).

The device power system 58 also includes a charge controller 60 that isconfigured to provide feedback control of the AC charging currentI_(CHG). In the example of FIG. 2, the charge controller 60 isconfigured to monitor an amplitude of a battery voltage V_(BAT) and anamplitude of the AC charging current I_(CHG) based on a charging voltageV_(CHG). The device power system 58 includes a sense resistor R_(S) thatis coupled to the primary inductor L₁ and ground, such that the chargecontroller 60 monitors the charge voltage V_(CHG) at a monitoring node62 that is coupled to the other end of the sense resistor R_(S). Thus,the charging voltage V_(cHG) has an amplitude that is proportional tothe amplitude of the charging current I_(CHG) through the primaryinductor L₁. In response to the battery voltage V_(BAT) and the chargingvoltage V_(cHG), the charge controller generates the DC feedback controlvoltage V_(FB) that has an amplitude based on a desired amplitude of thecharging current I_(CHG) based on a continuous amplitude of the batteryvoltage V_(BAT).

The device power system 58 also includes an isolation capacitor C₂ thatinterconnects the monitoring node 62 and the second conductor of thecharging cable 56. In the example of FIG. 2, the charge controller 60provides the DC feedback control voltage V_(FB) to the second conductorof the charging cable 56, which is thus added to the charging voltageV_(ChG) via the isolation capacitor C₂ to generate the control voltageV_(CTRL). Therefore, because the isolation capacitor C₂ provides DCblocking capability, the DC feedback control voltage V_(FB) does notaffect the amplitude of the charging voltage V_(cHG). The controlvoltage V_(CTRL) is thus provided to the AC adapter 52, and is thusprovided to the programmable AC current source 54. Therefore, theprogrammable AC current source 54 can set the amplitude of the ACcharging current I_(CHG) based on the control voltage V_(CTRL) in afeedback manner. Particularly, an average voltage across the isolationcapacitor C₁ in the AC adapter 52 can correspond to the DC feedbackcontrol voltage V_(FB) based on the DC blocking capability of theisolation capacitor C₁. Accordingly, the programmable AC current source54 can provide the AC charging current I_(CHG) at an amplitude thatcorresponds to the requested amplitude as provided by the amplitude ofthe DC feedback control voltage V_(FB) provided by the charge controller60. Accordingly, the battery B₁ can be charged rapidly in a closed-loopmanner based on the programmable AC current source 54 generating the ACcharging current I_(CHG) at an amplitude that is dictated by theamplitude of the battery voltage V_(BAT).

The battery charging system 50 can be implemented to charge any of avariety of electronic devices, and can implement any of a variety ofdifferent types of charging cables for the charging cable 56. Asdescribed previously, the charging cable 56 can be implemented as a USBcable, such that existing designs for USB cables and associatedconnectors can be used. As an example, one or more of the pins ofexisting USB cable and connector designs can be left unused, or can beused for additional control purposes unrelated to charging of thebattery B₁. Additionally, because the battery charging system 50implements charging based on an AC charging current I_(CHG), thepolarity of the charging cable 56 is irrelevant. Particularly, changingthe polarity of the charging cable 56 can change the polarity of thecontrol voltage V_(CTRL), but given that the programmable AC currentsource 54 can monitor the absolute value of the control voltage V_(CTRL)(e.g., based on the average voltage across the isolation capacitor C₁corresponding to the DC feedback control voltage V_(FB)), the polarityof the control voltage V_(CTRL), and thus the charging cable 56, isirrelevant. Furthermore, because of the simplified two-conductorconnection between the AC adapter 52 and the device power system 58,legacy USB cables, such as a USB Type-C cable, can be used in thebattery charging system 50 to provide backward compatibility withexisting charging cables.

FIG. 3 illustrates yet another example of a battery charging system 100.The battery charging system 100 can correspond to either of the batterycharging systems 10 and 50 in the respective examples of FIGS. 1 and 2.The battery charging system 100 includes an AC adapter 102 and a devicepower system 104. The AC adapter 102 can be configured substantially thesame as the AC adapter 52, and can thus include a programmable ACcurrent source configured to generate an AC charging current based on acontrol voltage. Similarly, the device power system 104 can beconfigured substantially the same as the device power system 58, and canthus be configured to convert the AC charging current to a DC chargingcurrent to charge the battery, and can generate the DC feedback controlvoltage that is provided back to the AC adapter via the control voltage.

In the example of FIG. 3, the battery charging system 100 includes aUSB-Type C cable 106 that interconnects the AC adapter 102 and thedevice power system 104. The USB-Type C cable 106 can implement aconnection of two conductors between the AC adapter 102 and the devicepower system 104, such that the first conductor can provide the ACcharging current from the AC adapter 102 to the device power system 104and the second conductor can provide the control voltage from the devicepower system 104 to the AC adapter 102. In the example of FIG. 3, theUSB-Type C cable 106 is demonstrated as having a coupling of an A₁₂ pinand a B₁ pin at each of a connector 108 associated with the AC adapter102 and a connector 110 associated with the device power system 104.Similarly, the USB-Type C cable 106 is demonstrated as having a couplingof an A₁ pin and a B₁₂ pin at each of the connector 108 and theconnector 110. The respective A₁ and B₁₂ pins and A₁₂ and B₁ pins can beelectrically coupled (i.e., shorted) in either the respective connectors108 and 110 or in the USB-Type C cable 106 itself.

As an example, the AC charging current can have a maximum amplitude of36 volts RMS, such that the AC adapter 102 can deliver 32 watts perampere RMS. For an AC resistance at 1 MHz that is four times greaterthan the respective DC resistance of the USB-Type C cable 106, thecurrent rating of the USB-Type C cable 106 can be de-rated by a factorof two. Therefore, assuming an approximately 90% power deliveryefficiency, the USB-Type C cable 106 can be configured to deliverapproximately 36 watts for a five ampere rating of the USB-Type C cable106, or to deliver approximately 21.6 watts for a three ampere rating ofthe USB-Type C cable 106. Therefore, the USB-Type C cable 106 can beimplemented as described herein to provide more rapid charging of abattery of a mobile device relative to typical battery charging systemswithout requiring a cable adapted for use with the battery chargingsystem 50, as described herein. Alternatively, a cable with a higherpower rating can be used in the battery charging system 50, as describedherein, to provide even more rapid battery charging.

In view of the foregoing structural and functional features describedabove, a method in accordance with various aspects of the presentdisclosure will be better appreciated with reference to FIG. 4. While,for purposes of simplicity of explanation, the method of FIG. 4 is shownand described as executing serially, it is to be understood andappreciated that the present disclosure is not limited by theillustrated order, as some aspects could, in accordance with the presentdisclosure, occur in different orders and/or concurrently with otheraspects from that shown and described herein. Moreover, not allillustrated features may be required to implement a method in accordancewith an aspect of the present disclosure.

FIG. 4 illustrates a method 150 for charging a battery (e.g., thebattery 20) associated with a mobile device. At 152, a power voltage(e.g., the voltage V_(LINE)) is received at an AC adapter (e.g., the ACadapter 12). At 154, an AC charging current (e.g., the AC chargingcurrent I_(CHG)) is generated based on the power voltage via aprogrammable AC current source (e.g., the programmable AC current source14) associated with the AC adapter. The AC charging current can beprovided on a first conductor of a charging cable (e.g., the chargingcable 16) that interconnects the AC adapter and the mobile device. At156, a control voltage (e.g., the control voltage V_(CTRL)) is receivedon a second conductor of the charging cable. The control voltage caninclude a voltage associated with the AC charging current (e.g., thecharging voltage V_(CHG)) and a DC feedback control voltage (e.g., theDC feedback control voltage V_(FB)). At 158, an amplitude of the ACcharging current is adjusted based on an amplitude of the DC feedbackcontrol voltage.

What have been described above are examples of the disclosure. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or method for purposes of describing the disclosure, but oneof ordinary skill in the art will recognize that many furthercombinations and permutations of the disclosure are possible.Accordingly, the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims.

What is claimed is:
 1. A battery charging system configured to charge abattery associated with a mobile device, the battery charging systemcomprising: a transformer configured to receive an AC charging currentvia a charging cable at a primary inductor and to generate an ACsecondary current at a secondary inductor; and a rectifier systemconfigured to rectify and filter the AC secondary current to generate aDC charging current that is provided to charge the battery.
 2. Thesystem of claim 1, wherein the AC charging current is provided via afirst conductor of the charging cable, the system further comprising acharge controller configured to monitor an amplitude of a batteryvoltage and an amplitude of the AC charging current, and to generate aDC feedback control voltage, the AC charging current having an amplitudethat is based on the DC feedback control voltage.
 3. The system of claim2, wherein the charge controller is configured to monitor the amplitudeof the AC charging current based on monitoring a voltage associated withthe AC charging current at a monitoring node, the system furthercomprising an isolation capacitor that interconnects a second conductorof the charging cable and the monitoring node, such that the chargecontroller adds the DC feedback control voltage to the voltageassociated with the AC charging current at the second conductor of thecharging cable.
 4. The system of claim 2, further comprising an ACadapter that is configured to generate the AC charging current based ona power voltage.
 5. The system of claim 4, wherein the AC adaptercomprises a programmable AC current source configured to receive acontrol voltage on a second conductor of the charging cable, the controlvoltage comprising a voltage associated with the AC charging current andthe DC feedback control component, the programmable AC current sourcebeing configured to generate the AC feedback control voltage in afeedback manner.
 6. The system of claim 5, wherein the AC adaptercomprises an isolation capacitor that interconnects a second conductorof the charging cable and a low-voltage power rail associated with theprogrammable AC current source, such that the programmable AC currentsource is configured to set an amplitude of the AC charging currentbased on an average voltage amplitude across the isolation capacitorcorresponding to the DC feedback control voltage.
 7. The system of claim4, wherein the charging cable is configured as a universal serial bus(USB) Type-C cable comprising a first connector coupled to the ACadapter and a second connector coupled to the mobile device, wherein anA₁₂ pin and a B₁ pin are electrically coupled at each of the firstconnector and the second connector, and wherein an A₁ pin and a B₁₂ pinare electrically coupled at each of the first connector and the secondconnector.
 8. The system of claim 1, wherein the rectifier systemcomprises: a plurality of transistors arranged as a synchronousrectifier bridge configured to rectify the AC secondary current; and anLC filter configured to generate the DC charging current based on therectified AC secondary current.
 9. The system of claim 1, wherein the ACcharging current is generated at a frequency that is greater than 500kHz.
 10. A method for charging a battery associated with a mobiledevice, the method comprising: receiving a power voltage at an ACadapter; generating an AC charging current based on the power voltagevia a programmable AC current source associated with the AC adapter, theAC charging current being provided on a first conductor of a chargingcable that interconnects the AC adapter and the mobile device; receivinga control voltage on a second conductor of the charging cable, thecontrol voltage comprising a voltage associated with the AC chargingcurrent and a DC feedback control voltage; and adjusting an amplitude ofthe AC charging current based on an amplitude of the DC feedback controlvoltage.
 11. The method of claim 10, wherein generating the AC chargingcurrent comprises generating the AC charging current at a frequency thatis greater than 500 kHz.
 12. The method of claim 10, further comprising:receiving the AC charging current via the charging cable at a primaryinductor of a transformer associated with the mobile device; generatingan AC secondary current via a secondary inductor of the transformer; andrectifying and filtering the AC secondary current to generate a DCcharging current that is provided to charge the battery.
 13. The methodof claim 10, further comprising: monitoring an amplitude of a batteryvoltage associated with the battery; monitoring an amplitude of the ACcharging current; and generating the DC feedback control voltage at anamplitude that is based on the amplitude of the battery voltage and theamplitude of the AC charging current.
 14. The method of claim 10,further comprising combining the DC feedback control voltage and thevoltage associated with the AC charging current on the second conductorof the charging cable that interconnects a first isolation capacitorassociated with the AC adapter and a second isolation capacitorassociated with the mobile device, wherein adjusting the amplitude ofthe AC charging current comprises adjusting the amplitude of the ACcharging current based on an average voltage across the first isolationcapacitor that corresponds to the DC feedback control voltage.
 15. Abattery charging system comprising: an AC adapter comprising aprogrammable AC current source configured to generate an AC chargingcurrent having an amplitude that is based on an amplitude of a DCfeedback control voltage; and a device power system associated with amobile device, the device power system comprising: a transformerconfigured to receive the AC charging current via a first conductor of acharging cable at a primary inductor and to generate an AC secondarycurrent at a secondary inductor; a rectifier system configured torectify the AC secondary current to generate a DC charging current thatis provided to charge a battery associated with the mobile device; and acharge controller configured to monitor an amplitude of a batteryvoltage and an amplitude of the AC charging current and to generate theDC feedback control voltage that is provided to the AC adapter via asecond conductor of the charging cable.
 16. The system of claim 15,wherein the charge controller is configured to monitor the amplitude ofthe AC charging current based on monitoring a voltage associated withthe AC charging current at a monitoring node, the device power systemfurther comprising an isolation capacitor that interconnects the secondconductor of the charging cable and the monitoring node, such that thecharge controller adds the DC feedback control voltage to the voltageassociated with the AC charging current at the second conductor of thecharging cable.
 17. The system of claim 15, wherein the AC adapterfurther comprises an isolation capacitor that interconnects a secondconductor of the charging cable and a low-voltage power rail associatedwith the programmable AC current source, wherein the programmable ACcurrent source is configured to receive a control voltage on the secondconductor of the charging cable, the control voltage comprising avoltage associated with the AC charging current and the DC feedbackcontrol component, the programmable AC current source being configuredto generate the AC feedback control voltage in a feedback manner basedon an average voltage amplitude across the isolation capacitorcorresponding to the DC feedback control voltage.
 18. The system ofclaim 15, wherein the charging cable is configured as a universal serialbus (USB) Type-C cable comprising a first connector coupled to the ACadapter and a second connector coupled to the mobile device, wherein anA₁₂ pin and a B₁ pin are electrically coupled at each of the firstconnector and the second connector, and wherein an A₁ pin and a B₁₂ pinare electrically coupled at each of the first connector and the secondconnector.
 19. The system of claim 15, wherein the rectifier systemcomprises: a plurality of transistors arranged as a synchronousrectifier bridge configured to rectify the AC secondary current; and anLC filter configured to generate the DC charging current based on therectified AC secondary current.
 20. The system of claim 15, wherein theAC charging current is generated at a frequency that is greater than 500kHz.